1. Field of the Invention
The present invention relates to a method and a system in which information processing devices connected to the same local network can securely communicate with each other. In this local network, information processing devices can directly communicate with each other without a data relay device known as a router.
2. Description of the Related Art
In known communication methods and systems, when information processing devices connected with each other via any communication means carry out data communication, a global address is used. A global address is disclosed in, for example, a document by R. Hinden, M. O'Dell, and S. Deering, July 1998, available at the Internet:<URL:http://www.ietf.org/rfc/rfc2374.txt>. A global address is a unique network address not only in the same network but also in different networks. When an information processing device is connected to the same network as a target communication information processing device and can directly communicate with the target communication information processing device without a router, a link-local address is used. The link-local address is disclosed in, for example, a document by R. Hinden and S. Deering, April 2003, available at the Internet:<URL:http://www.ietf.org/rfc/rfc3513.txt>. Although a link-local address is unique in the same local network, the uniqueness of link-local address is not guaranteed in different networks.
However, in the known technologies, when an information processing device uses a global address for data communication, an information processing device belonging to a different network can connect to the information processing device. Accordingly, if a malicious user happens to know the global address of the information processing device, the malicious user could start a Denial-of-Service (DoS) attack against the information processing device. The DoS attack disables the communication of the information processing device by continuously transmitting a large amount of data. Also, global addresses are widely disclosed by a DNS (domain name service) and are fixed numbers. Thus, the communication using global addresses is vulnerable to sniffer attacks, which is a problem.